cho tam giac ABC can tai A
lay trung tuyen BM, Cn h la hiem giao nhau giua 2 trung tuyen BM va CN.
a/cm AH cat BC tai trung diem cua BC.
b/lay diem F tren tia doi CN, diem E tren tia doi BM. CM:F,A,E thang hang tu do => FE // BC
day la level 0 nen rat de co gang nhe